1. Field of the Invention
The invention relates to an arrangement and method for sealing of a pocket space between drying cylinders in a paper machine or similar as presented in the preamble of the independent claim presented below. The invention particularly relates to a new manner of arranging air blows in the pocket space. The invention also relates to a runnability component of a paper machine and to a method for manufacturing the same.
2. Description of the Prior Art
In a typical dryer section of a paper or board machine the web to be dried is conveyed, supported by one or two wires, via hot drying cylinders. The tendency of the web to detach from the surface of the drying wire thus causing runnability problems has presented a problem. Especially problematic in this connection are the following points                so-called opening nips, i.e. locations where the web and the wire detach from the drying cylinder. In this case, the web has traveled between the wire and the cylinder, and as the wire detaches from the cylinder, the web tends to follow the surface of the cylinder and then detach from the wire; and        so-called closing nips, where the web and the wire are brought into connection with the cylinder. In this case, the web tends to detach from the wire due to an overpressure formed in the nip.        
Opening and closing nips exist both at the drying cylinders and between them, and usually in connection with the lower turning cylinders or turning rolls.
Detachment of the web from the wire easily leads to a web break or at least to formation of pouches or cockles in the web. Detachment of the web from the wire thus leads to runnability problems, which problems are further emphasized when the speeds of the paper machines increase.
It is previously known to use different kinds of runnability components, such as blow boxes, for improving the runnability of a paper machine. A component improving runnability has been presented in the American patent publication U.S. Pat. No. 4,905,380, which presents a blow suction box to be used in a multi-cylinder dryer of a paper machine. With an ejection blow created with the blow box, an underpressure zone is induced in the gap space between the drying wire and the wall of the blow box, which underpressure zone keeps the web attached to the drying wire as the web travels from the drying cylinder to the turning roll below it. The underpressure zone is obtained in the gap space on the exit side of the drying cylinder with an ejection blow against the travelling direction of the wire. Respectively, an underpressure zone is created or it is intensified on the exit side of the turning roll below the drying cylinder, in the gap space defined by the drying wire and the wall of the blow suction box, with an ejection blow in the travelling direction of the drying wire.
The solution described above however presents the problem of arriving to safely seal the underpressure zone induced with blows from the area remaining outside the zone. In connection with malfunction, paper waste is created in paper machines, which paper waste often forms paper clods or wrinkles in the web, which cause problems in narrow points of the machine, e.g. in the narrow spaces between blow boxes and wires, cylinders or rolls. Due to paper clods travelling along with the web to be dried and with the wire, or due to other corresponding bulges appearing in the web, the blow box can not be mounted at a desired short distance from the moving wire. Fairly great safety distances are required between wires and blow boxes for that said bulges could travel along with the wire by the blow box without touching it and without damaging its constructions or the wire. As the blow nozzles of the blow boxes need to be placed at said safety distance from e.g. the wire, the effects of the ejection blows often remain insufficient. The underpressure zone is also not sealed well enough.
This problem has been solved e.g. in the patent publication U.S. Pat. No. 6,247,247 B1. The publication presents a sealing element, such as a blow nozzle, arranged at the border of the desired underpressure zone and the area remaining outside the zone, protruding from the blow box towards the wire and to a given distance “d” from the wire, in order to form a seal between the underpressure zone and the area remaining outside of the underpressure zone. The sealing element is connected to the blow box such that the element can be moved away from the wire by pressing and/or with the aid of an actuator, to a distance “D”, which is greater than the distance “d”. The solution is working, but however, air leaks by the sealing. This in turn causes undesired energy consumption.
The prior art runnability components, such as blow boxes are not quite straight in their longitudinal direction, i.e. in the cross direction of the machine. The bending of the runnability components is usually a few millimeters. This is one of the reasons for which it has not been possible to bring the sealing elements very close to the wire.